Patent Literature 1 discloses an example of a sensor for use with an automatic door having a plurality of two-dimensionally arranged detection areas. According to the technology disclosed in Patent Literature 1, light emitting means is used to project spotlight to form spots of light in a matrix on a floor near a door of an automatic door system. Light reflected from each of the light spots on the floor is received by light-receiving means. If light from any one or more of the light spots is interrupted, it is judged that a human is detected, and the door is opened based on the judgment.